Scanning electron microscope (SEM) ELECTRON SOURCES

Ruth Jaimes 2013

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Hitachi S-4800 field emission scanning electron microscope

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1. What is the main idea of SEM?

2. Electron gun

3. How is a fine electron bean formed?

4. Haw can we obtain an even finer electron bean?

5. What kinds of electron guns (electron sources) are used in the SEM?

6. What are the differences between the kinds of electrons guns?

ELECTRON SOURCES

SEM ELECTRON SOURCES

The electron gun are located either at the very top region of the SEM that generates a beam of electrons

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A scanning electron microscope (SEM) is a type of electron microscope that produces images with a focused beam of electrons.

The electrons interact with electrons in the sample

The electron beam is generation by electrons sources.

Configuration of SEM

The mechanism that emits electrons form a metal and accelerates them a strong electric field.

1. What is the main idea of SEM?

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How is a fine electron bean formed?

The electron source (diameter do) formed by electron gun is reduced and made into a fine electron bean (diameter dk) by the condenser lens and objective lens.

Haw can we obtain an even finer electron bean?

In order to obtain a fine electron bean,the instrument utilizes an electron gun featuring: a small electron source, a large current density (current (in A/cm2) per unit area, and a small energy width (energy vitiating (in eV) of discharged electrons.

SEM ELECTRON SOURCES

Why is important the electron sources?

The simplest and cheapest gun uses a heated tungsten wire to produce electrons.

generates a beam of electrons

What kind of electron sources is used in the SEM?

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Field emission guns, create a strong electrical field to pull electrons away from the atoms.

Thermionic guns type, apply thermal energy to a filament (usually made of tungsten, which has a high melting point)

- cold field emission, - Schottky,

- tungsten, - LaB6 (lanthanum hexaboride)

There are three types of electron gun according to the method of emission: - field emission type (FE) electron gun, - Schottky electron gun and, - thermal electron gun.

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What kind of electron sources is used in the SEM?

(a) Thermionic gun (tungsten)

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What kind of electron sources is used in the SEM?

(b) LaB6 gun

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What kind of electron sources is used in the SEM?

(c) cold field emission (FE) electron gun

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What kind of electron sources is used in the SEM?

(d) Schottky electron gun

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What are the differences between the kinds of electrons guns?

SEM ELECTRON SOURCES

CAMTEC Nanofabrication Workshop

CAMTEC Nanofabrication Workshop

Thanks for attention

Canada

Brazil

Victoria BC